As far as the pick goes, the conditions of the deal are that Vancouver gets Portland's first round pick in the first bantam draft after Grimaldi reports to Portland. So if he reports for this coming season, it's the 2012 pick. If he reports for 2012-13, then it's the 2013 pick. Not sure what happens if he reports for 2013-14 only, but he'd be an overager that season so it's very unlikely that would happen since he could go to the AHL at that point instead.
Personally I think it's a longshot that he ever plays in the WHL. He's headed for North Dakota next season and that's a top hockey school. He's also going to be a first round pick in the NHL draft so he'll have serious pro options if he wants to leave school after a year or two. And he's also only 5'6" so the rougher, more physical style of major junior may not suit his development as well as the college game does. I think he's a guy who plays two years of NCAA and then signs his NHL deal. But that's just my opinion.