Vancouver businesses are at an inherent disadvantage compared to Portland ones regarding the need to charge sales tax. Why not create a "same everyday low prices, and we pay your sales tax" zone?
If a large big-box chain started this, what would be the result? Less profit per item, but increased sales volume from both Oregonians and Washingtonians and increased bottom line profit.
The key would be consistency, with stores displaying a standardized emblem showing they're with the program. Stores and businesses would fill with people, and then draw in even more. Washington's sales tax revenue would increase, commerce would increase here in the Couv, and all shoppers from both states would get the benefit of increased competition.
Everybody could feel good, make and/or save more money, and government would be better supported, without a need for any new legislation.