Probably. Generally speaking, Canadian border officials do not deny entry to someone with a pending DUI from Washington State. That said, you should not provide specific details about your pending DUI charge. If you admit sufficient information to a border official about a pending Washington State DUI or Physical Control case you may be denied entry even though not convicted. In other words, do not lie or misrepresent information, but be very careful about volunteering too much information. I have had many clients with a pending DUI case cross the border. Some were - and some were not - asked about the pending DUI charges. Obviously, if they are asking you about a DUI charge - they know about it.
As a courtesy, I provide clients with a letter for the Canadian border official with a basic summary of the procedural status of the case - just in case they are asked questions about the pending matter. Unfortunately, Canadian border officials have wide discretion in denying entry - which means there are no gurantees.
