You said to Canada and you'll have to abandoned 101 at some point to get there. The most scenic and best route would be to follow 101 on the west side to Port Townsend and then take the ferry to Coupeville, and hook up with I5 just beyond Deceptions Pass. Your other alternative is to take Hwy 3 off 101 and take the Narrows Bridge over to Tacoma and then to I5 or go almost all the way around to Olympia and catch I5 there Going through Seattle isn't fun, but once through, youll have beautiful sights and wonderful campgrounds. The ferry will cost about $70-80 bucks, the price of the Narrows is going up and I'm not sure what it costs for an RV and going to Olympia is doable but you have to deal with traffic from there up and thru Everett WA.