C-GEML, a Diamond DA 20-A1 aircraft operated by Sea Land Air Management, was conducting a scenic flight from Vancouver/Boundary Bay, BC (CZBB) to Squamish, BC (CYSE) and return with two people on board. While retuning from CYSE, the pilot observed an engine vibration (Rotax 912 S3). The pilot attempted unsuccessfully to troubleshoot the source of the vibration. While in the vicinity of Point Atkinson, BC, the pilot contacted ATC and requested a direct route back to CZBB. Since they were unable to provide a direct route, ATC then offered Vancouver Intl, BC (CYVR) as an alternative. The pilot declared an emergency and diverted to CYVR where a landing was made without further incident.