Point Roberts -
Ok not technically Lower Mainland because it's in the US, but Maple Beach is literally steps away from Canada! Point Roberts is usually pretty quiet, but in the summer this beach can get busy with lots of other fellow paddle boarders. I went during high tide so the water was easy to get to and shallow enough that the ocean was actually warm to swim in. If you go at low tide, it's a bit of a walk to the water.
Ps, this is my moms first time on the sup, isn't she cute?