DURING A VFR CROSS COUNTRY FLIGHT ON A VFR FLIGHT PLAN FROM BOUNDARY BAY, CANADA, TO SEATTLE, WASHINGTON, THE CANADIAN REGISTERED PIPER PA-23-250 WAS INVOLVED IN A MID-AIR COLLISION WITH A CESSNA 172 THAT WAS OPERATING ON AN IFR FLIGHT PLAN, PRACTICING APPROACHES AT EVERETT, WASHINGTON. THE COLLISION OCCURRED AT 2,200 FEET IN VMC. THE CESSNA WAS PERFORMING A MISSED APPROACH PROCEDURE AND HAD BEEN INSTRUCTED TO TURN TO 70 DEGREES AND MAINTAIN 2,000 FEET. THE CANADIAN AIRPLANE WAS TRAVELLING IN A SOUTHERLY DIRECTION OPERATING BELOW AN OVERCAST LAYER IN VMC. THE CANADIAN AIRPLANE WAS NOT IN COMMUNICATION WITH ATC AT THE TIME. THE CESSNA WAS IN COMMUNICATION WITH SEATTLE ARTCC AND WAS AWAITING FURTHER INSTRUCTIONS WHEN THE COLLISION OCCURRED. POST-CRASH TOXICOLOGICAL TESTING REVEALED THAT THE PILOT TESTED POSITIVE FOR TETRAHYDROCANNABINOL IN BLOOD AND THC IN BLOOD AND URINE.