One of the former common drug related offences in Canada had invariably something to do with Marijuana / Cannabis / Reefer / Mary Jane / Grass. In case you have been booked by the police for using or distributing drugs of any kind, the sentence could be really catastrophic and its impact on your personal life even more disastrous.
A Conviction could also mean that you now have a criminal record which could limit your travel scope, especially crossing over to the U.S and at the same time it will certainly reduce job opportunities in the future. You need to understand that it is irrelevant that Washington State or even Canada legalized Marijuana. The U.S. Border (C.B.P) follows U.S. federal information, where Marijuana is still listed as an illegal drug.
If you have admitted having smoked, carried or distributed marijuana to a CBP officer, chances are you will need a waiver to enter U.S. In short, you can be categorised as an individual who is inadmissible. Remember, drug abuse may lead to a criminal record as it is considered an offence.