Translink in Vancouver area has very few double decker buses on the road from what I've seen so far in over a year living here, but it looks like more will be introduced.
There is opposition and decisions not to accept double decker buses in White Rock because it will reduce the tree canopy significantly in order to operate safely. Also some trees would need to be removed completely.
I agree the canopy impacts beauty and livability of cities, house values etc. I wouldn't support removing many ancient trees that make our city breathable for adding taller buses.
Personally I don't like double decker buses much from my experience in Ireland. Climbing down a stairs to leave the bus is annoying and dangerous as bus moves and jerks suddenly.
If you're not downstairs or on the way downstairs by the stop you might not be able to disembark from my experience in Dublin. You're expected to come downstairs while the bus is moving so you are ready to get off.
A recipe for disaster if you ask me!