Baseball is back.

MLB and the players union reached a new collective bargaining agreement Thursday afternoon, and the lockout ended after 99 days when the owners unanimously ratified the labor deal.

Sunday is the mandatory report date for spring training training. In the meantime, buckle up. The Cubs and MLB's other 29 teams now face a frenetic, action-packed finish to the offseason leading up to Opening Day.

When MLB implemented the lockout on Dec. 2, we were in the middle of one of the most active Hot Stove periods in recent memory. The lockout brought a freeze to all big-league transactions.

The transaction freeze was lifted Thursday night, allowing free agency to reopen and clubs to make trades.

With Opening Day scheduled for April 7, there's little time for teams to conduct months’ worth of moves before the season.

Again, buckle up.

Here's what the Cubs still have left to do before the regular season begins.

Roster filling

We’ll use roster filling here as a general term for additions via trade or free agency. 

The Cubs made several moves before the lockout, signing catcher Yan Gomes, outfielder Clint Frazier and starter Marcus Stroman — their headline addition to date.

RELATED: How Stroman landed with Cubs after whirlwind week

They still have other holes to address and less time to do so, including shortstop, maybe a power bat, a starting pitcher (or two) to compete for a back-end rotation spot(s), and a veteran presence for the bullpen.

Carlos Correa would address the former two needs, and the Cubs had mutual interest with him before the lockout. Whether they go to the top of the market for him is a big question, and it may take them getting creative to add any of the big-name free agents left on the board. 

The Cubs signed Stroman to a three-year deal with high average annual value, and a report from earlier in the lockout suggested they were interested in Correa on a seven-year deal.

That report came before Correa hired Boras, the top-grossing agent in baseball whose clients historically maximize their free agencies. 

If Correa somehow wasn’t already bound for a massive deal, he certainly is now. Assuming he signs elsewhere, Trevor Story would be the obvious Plan B — if the Cubs go big. 

Other shortstop options include free agents Jose Iglesias and Jonathan Villar, and potential trade candidates Nick Ahmed (Diamondbacks) and Isiah Kiner-Falefa (Rangers) — after Texas signed Corey Seager and Marcus Semien to lucrative multi-year deals before the lockout.

MORE: Free agents? Try these 3 trades on for size instead, Cubs

Arbitration

The arbitration process will carry into the season, which there's precedent for after a work stoppage. It happened in 1995, after the union's strike.

For the Cubs, that’s relevant as it pertains to Willson Contreras and Ian Happ, who were tendered contracts before the lockout but are arbitration eligible.

In a normal offseason, teams and arbitration-eligible players have until mid-January to agree to a salary for the coming season. If they don’t reach an agreement, each side submits a figure for a February hearing with a panel of arbitrators.

MLB set March 22 as the exchange date, according to The Athletic's Ken Rosenthal, and hearings will happen during the regular season.

That not only could cloud a team’s respective payroll situation, but obviously some players could be taking the field without knowing their salary.

Happ took the Cubs to a hearing last winter — the club’s third since 1993 — and won. It was the first time the Cubs lost an arbitration case since 1990 (Shawon Dunston).

Trades

Speaking of Contreras and Happ, they stand as two of the Cubs’ biggest trade candidates.

Contreras is entering his final season of club control and is the last member of the Cubs’ homegrown, position player championship core left following last summer’s trade deadline selloff. 

If the Cubs don’t intend to extend him (more on that in a bit), it would make more sense to deal him before the season to maximize the return.

Happ is coming off an up-and-down season in which he experienced a career-worst slump at the plate the first four months before finishing strong.

With the roster at a transition point, this year could be decision time for the organization on Happ, whether that’s this spring or during the season. He’s yet to demonstrate he can put together a full season of production.

MORE: Impact decision for Cubs: Embrace Ian or play Happ-less

Contract extensions

Did someone say Contreras and extension? 

The Cubs had not broached those talks with their starting catcher by the time the lockout hit, but he’s as much of a building block as anybody on the roster for the team’s current transition and next competitive window.

Contreras indicated last season he’s open to the team building around him going forward. He also told NBC Sports Chicago in separate conversations he wants to see the front office’s plan and direction before signing a new deal, whether they have interest in offering him one or not.

The Cubs historically have conducted extension talks in spring training, though whether the condensed timeline changes that is uncertain right now. 

Assuming the Cubs want to build around the two-time All-Star starter and clubhouse leader who brings a competitive edge day in and day out, it would be wise to get those talks going as soon as possible.

While we’re on the subject, the Cubs have had preliminary discussions with manager David Ross about an extension, team president Jed Hoyer said in October. Ross is entering the final year of his original three-year contract.

Teams were allowed to make hires and negotiate extensions with managers and coaches during the lockout. It won't be surprising if the Cubs announce a Ross extension in the coming days.

Rule 5 Draft

Update: This offseason's Rule 5 Draft has been canceled.

The minor league portion of the Rule 5 Draft was held in December because those players are not subject to 40-man roster rules and the transaction freeze. 

But the big-league portion was delayed due to the lockout. It typically occurs during the Winter Meetings, which were canceled.

The Cubs have roster flexibility with where they are in their process and could have a greater luxury of carrying guys who don’t have to be major contributors in the short term. That could include a Rule 5 pick sticking on the roster.

The last time the Cubs went through a transition, they selected Héctor Rondón in the Rule 5 Draft (2012). He made 45 appearances in 2013 (4.77 ERA) before blossoming into the team’s closer and a key reliever during their 2015 and 2016 playoff runs.

There's also at least a chance the Rule 5 is canceled entirely. Some clubs reportedly asked the league about that possibility recently amid the lockout's uncertainty.

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