A team can go up to $4.3m on Cernak and only give up a 2nd round pick. Assuming the Leafs don't give up their 2nd in the Campbell/Clifford deal, and they believe Cernak can be a guy that plays regularly on the top pair with Morgan Rielly, there's absolutely no reason why they can't go give Cernak a 4 year deal at $4.25m and make Tampa's life very difficult, as they probably envision him more towards a 2 year deal at $2m/season.
The problem for the Leafs in doing this -- is that it will tie up their limited cap flexibility for 10 days, and potentially mean that they miss out on another opportunity while waiting to see if Tampa matches.
As a result, it cannot be a primary plan for the Leafs, more likely something that happens as a plan C or D or E in late July.
That being said, there are 29 other teams out there... and he would be prime picking for an offer sheet if he wants to prioritize some job security rather than waiting to maybe hit a home run in 2 years.