Vancouver didn't really have the option of keeping Schneider as a backup for any longer. He wanted to become a #1 and his play showed he deserved this. His contract was up for renewal, and the fact the Canucks signed him to 4 million deal shows that he was signed to become the #1 goalie.
I actually think (as much as I think the guy is a wicked goalie) that trading Schneider might have been a viable option at one time. But now, you don't just sign a guy to three years and then trade him. As a result, the only options left are to play Luongo as a backup (which is both a waste of cap space as well as talent, besides being controversial), or trade him.
Many people seem to think the contract is a big issue, but I really don't think it is. The cap hit is reasonable and I actually think the long contract is a GOOD thing for a team, as long as Luongo continues to play at a high level.
However, those who say that Gillis is the one who will have to make concessions in a trade are entirely correct... but not because of the contract. It is because the only realistic option for Vancouver right now is to trade Luongo, and other GMs know it. Add to that the fact there are only a couple of teams that really need a goalie, and that drives down the return that much more. Under different circumstances, a star goalie would garner a star player in return. But unfortunately for Gillis, it isn't going to happen in this case... yet, he's holding out for the best return he can get.
Add to all this the fact that Vancouver really needs a 2nd line centre right now with Kesler out, and the pressure is even higher for Gillis.
I still say though, without giving up any young talent like Gardiner (which isn't going to happen), that Luongo would be an excellent aquisition for the Leafs. Assuming, of course, they expect to be competetive right now. If they plan to rebuild, then they are better off with the two questionable goalies they have right now.