If you were referring to the Georgia Strait Current Atlas, it's of limited use for where you are. You will be needing the current tables specifically for First and Second narrows to time your passages. The real current atlas is somewhat cryptic and mostly of use to long distance racers and tugboat skippers.
There are advantages to keeping a boat in Pt Roberts, esp proximity to the Gulf Islands but constantly crossing borders is a hassle, and many there cruise exclusively in the US as a result. That in itself is neither good nor bad, but you'll miss an awful lot of beautiful territory on our side.
That 3 hp engine is going to be a bit of a problem if you intend to get yourself out to Georgia Strait. btw - you should give the False Creek Harbour Authority (604 733 3625) a call, they may well accommodate a 20 footer at rates similar to the North Shore. They are between Granville Is and Burrard Civic.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"