Honestly, I don't think +60 is even close to being realistic. there reasons are as many already mentioned, the style of game, long trips, long seasons, but the biggest difference will be the size of the rink. It takes away the parts that benefit granlund the most, time and space. Even on the pp there will be less time and space to work with. Personally i don't think he can go over 55 and might get only 30, in the worst case scenario. I think 35-50 is realistic, it will depend a lot on how much PP he plays.
Btw, the comparison to Kane and Nugent-hopkins is not fitting here, since they played in small rinks before NHL.
Some people claimed that he has adjusted well before, but the transition from A-junior sm-liiga --> sm-liiga is not nearly as big as sm-liiga-->nhl in traveling, amount of games per season, size of rink(the same actually) etc. And the WC was played in similar rink to sm-liiga. this also makes the comparison to NHL players a bit questionable.
I think he will have a great career, but offensively he won't come near Selänne and probably won't ever have a +90 point season, a couple 80 points season perhaps. And that would make me extremely happy. Great player.