Toronto needs a true top D-man to win the cup and this roster doesn't have one. Rielly isn't that guy, at least not yet. His 52 points was great progress but he needs a larger presence on the ice as a whole to crack that top tier. A look at past cup winners:
Caps: Carlson
Pens: Letang
Hawks: Kieth
Kings: Doughty
Bruins: Chara
I wouldn't put Rielly alongside those names yet

I don't get the idea of trading away Gardiner because of one bad game. You don't upgrade your d by trading away your #2 guy for another might be #2 guy. You need to use other assets to obtain a dman without losing one in order to upgrade the top4.

"one bad game" LMAO....have you watched Gardiner play in the last 6yrs? he's a nightmare in his own end, always has been, and it seems always will be, maybe he's not smart enough to grasp defense? who knows, yes he has 52 pts or whatever it is, Doughty has never had a season over 60pts, yet he makes almost 3x what Gardiner makes....hmmm wonder why? id trade Gardiner for whatever you can get for him,
not sure if you are old enough, but when the Leafs had Larry Murphy in the 90s, he had a 60+point season as was not only booed off the ice, he was booed out of town, he couldn't play "defence" with Toronto, just like Jake, get him out of this system now package him w/extras (leivo etc) and get whatever anyone is willing to offer.

The Ducks don't trade the long term contract of Manson for one year of Gardiner. That list is of top Dmen is nice but,,,,,,,the Pens won their last Cup without Letang, Vegas went to the Cup without a top defender.
If having a top Dmen is the panacea for success, look at Karlsson playoff appearance totals an the Sens playoff success. Hedman and Tampa have had irregular regular season and playoff success, Doughty has won two Cup but has first round exits and non playoff years.
I just think that the "top Dman = Cup" is more of an urban myth than fact.

Pittsburgh 1st of the back to back cups, and their most dominant win, happened with Justin Schultz as their #1 defenceman since Letang missed the entire playoffs. Rielly is a lot better than Schultz. What TO needs is a guy who can play with Reilly and compete against top level offensive players. They don't need a top 5 defenceman and to be honest, Carlsson is great offensively but he's not the best defensively and doesn't even get the tough minutes in Waskingotn that's Matt Niskanens (Or however you spell his name) job. So I think the whole the Leafs can't win without a stud D is not entirely correct.

Top D = Cup isn't the end all, it is just a very large contributing factor. The thing with Pittsburgh and that first cup is those D played within in themselves and understood they needed to move pucks up to that stacked offensive core. Toronto needs a D who can move pucks really well and be a shutdown guy to absorb those tough minutes. Vegas making it to the cup final came because the whole team was committed to defense which I don't see this Toronto group doing. W Karlsson was plus 49 this reg season, which Leaf is going to be anywhere close to that. If the full team is not committed to all out Defense they need a guy who can play 26+ minutes a night