driving to visit Vancouver Canada Place from Seattle - is it better to go on weekend or weekday from traffic perspective?
The wait for Canadian and US customs can be murder on the weekends.
You can get some border traffic info online and there will also be road signs suggesting alternate routes and wait times as you approach the border. Review alternate routes ahead on your map so you'll be comfortable choosing from those options.
Definitely the week days are faster. I'm in Langley, BC tonight, and it was only a 5 minute wait at the border Tuesday morning at 11:00 am.
As someone else mentioned, the border waits on weekends can be LONG (especially on holiday weekends in either country). You could perhaps use one of the other border crossings (Aldergrove, Sumas) although that will mean a drive over the Port Mann toll bridge. There's another route through Surrey that avoids the toll bridge, but unless you're familiar with the area, it would be best to stick with the most popular routes. As you're going to downtown, the Peach Arch crossing would be the most convenient.
Hopefully you won't have much trouble finding parking. One option might be to park in Surrey or one of the suburbs and take the SkyTrain. I'll leave it to someone from the lower mainland to suggest the best route.
You can take a train between Seattle and Vancouver.