I'm a vancouverite, there are so many things to do!
Everything mentioned are great suggestions!
As far as workout activities if you were interested: walking the seawall in Stanley park (a huge park in the middle of the city) is one of the most popular activities among locals, jut going to the park is a must do for any tourist. Or for an intense experience there's a hike called the Grouse Grind. Amazingexperience and a mega mega calorie burn lol. Or at least, if you can, take the gondola up grouse mountain, it's maybe a half hour from the city's downtown, many shuttles leave the city to take people up there. It's absolutely worth it.
Lastly, granville island is a part of the city that's very easy to get to, and is one of my favourite places to go. Those are my very top 3 suggestions.
Stanley park and Granville island is free. Grouse mountain does coat money to take the gondola but is free if you hike up
Driving across the border is very easy. It could be a 10-45 minute wait. Depends on the time of day. Then they just ask a couple of questions and you're through. Have fun!