I think it all depends on the definition of 'hated'.
On ice product/players? Yeah, I can see the Bruins being pretty unpopular among both players and viewers. They have Marchand and all.
Hated team because of fans/tradition? Yeah, I can see Toronto being up there. Even though the bad apples are a minority as with all fanbases, when there's so many fans you will have a large amount of bad interactions with the bad apples and it can get to you. When I started following the NHL and lurking here a bit over 10 years ago I had no idea why the Leafs were so hated - I didn't grow up with the idea that the Leafs are something to be hated. When I had some critique towards them, I got responses like "keep on being a Leafs hater" and I had no idea what the hell that was about - they were just another team among others, nothing special. I didn't 'hate on them' just because I was supposed to, I just had something to say that wasn't all positive. After years of such interactions the idea of hating the Leafs (or well - the fanbase, albeit unfairly to a large amount of them) grew on me.