Ok, since we're talking about an MLB franchise here, we're obviously dreaming at least a little bit. So I took that and ran with it.
In this alternate reality where Vancouver could actually support an MLB team, Translink/CoV has found 2 billion dollars under the cushions and built the Waterfront Transit hub, and CP rail has no problem with a massive retractable roof sitting over their train yard during the summer. Slightly more believable, the convention centre has expanded east and the Heliport has been relocated up above a new Seabus terminal to connect with Canada Place Way, Granville and Richards Street extensions. Obviously this alternate reality also supports a couple 400+ foot office towers around/above the transit hub.
The stadium is modelled after Fenway (I'm a big BoSox fan) but it's flipped to emulate AT&T park in San Fran a bit, with the green monster giving way to the Pacific where small boats and kayaks can sit to catch home runs (while avoiding Seabuses, Tugs and Cruise Ships). It would also be open to look over the water and the North Shore mountains. The field would have to be natural grass and would be adaptable for soccer (like Safeco). The roof modelled directly off of Safeco as well, moving over the tracks when not needed. What would be really sweet is if it could be made out of peaked fabric like Canada Place. Right-Centre field would also be able to hold a stage and host concerts (like Kerfoot's vision for his waterfront stadium). The site would have to be heavily piled (like VCEC West) but would have a level or two of parking between the Canada Place Way level and Waterfront Road level (how much I'm not sure, I would sink the field level down a bit so you walked in off of the plaza to the same grade as the 1st level concourse). The Seawall could be continued either around Canada Place or have it join up from a Granville Street. It would continue only as far as the Heliport and then link back through the Stadium Plaza onto Richards Street and then past Steamworks and into Gastown.
Who wants to lend me $10 billion?
edit: Yes, that roof is quite a bit bigger than Safeco, and yes it does completely cover the seating and playing field area.