A vast overpayment by Leafs. Vlasic has only one year left on his contract. JVR for Vlasic fine but no more.

well, maybe ... I dont think JVR alone is going to get the Leafs a top pairing defenseman.
so maybe JVR + mid level prospect + 2nd or 3rd round pick.
JVR + 2nd + ?

and let's be realistic... San Jose is not likely going to let Vlasic go straight up for JVR.
other comparables
Carolina - Jeff Skinner straight up for Vlasic?
Columbus - Cam Atkinson straight up?
Nashville - Arvidsson ?
Ottawa - Hoffman?
Philly - Vorachek?

If Vlasic was on Leafs - I wold not trade him straight up for JVR. I would want more, I think its close

Other thoughts?

Vlasic would normally be a good fit with the Leafs, however, we do already have two LHD who are paid to play big minutes: Gardiner and Rielly. Moreover, we have lots of depth in terms of left-handed Ds, with Dermott and the two Swedish acquisitions. With this trade, we lose our top left winger, and create a gaping hole on that side.

I guess trading Gardiner for Vlasic would avoid tampering with the balance of the team. One for one. I don't see why either team would do it, though, unless San Jose knows Vlasic intends to leave. Vlasic is better in the short run but 4 years older, and UFA in one year. Though he is what the Leafs would need next season, Gardiner could still improve and reach his prime in the next few years.

I think a trade with SJS would be for a guy like P.Martin, he is 36 with 2 yr left contract which cap can be digested.
He is a experienced left hand but plays RHD and would play 3rd pair RHD on the leafs and PK which we lack at the moment.
The issue is that his cap hit is way too high for a 3rd pair D, even though he could go up in case of injuries, and there are other cheaper options. If SJS keeps some cap and return is not too high could be an option for the short term though.