Hi Vincent - You can be pretty much guaranteed to see lots of Bald Eagles and, if you’re lucky, some of them will be nesting so perhaps you will see an eaglet or two. They can be found in many local parks in the Vancouver area (Stanley Park, UBC area, just about anywhere there is water) but especially at Boundary Bay (in Delta) and the surrounding area. If you drive along 72nd Street toward Boundary Bay you should be rewarded with many of them, in all stages of life, flying overhead and perched in the trees.
The George C. Reifel Migratory Bird Sanctuary is a must-see for any birder visiting here. Again, eagles will be plentiful and the Sanctuary itself will be loaded with all types of birds. Here’s their website: http://www.reifelbirdsanctuary.com/
Of course I can’t go without mentioning the Orphaned Wildlife Rehabilitation Society (OWL) in Delta (on 72nd Street, right in the middle of eagle territory) because I volunteer there. They are open for public tours on Saturday and Sunday only, from 10 am to 3 pm. There you can see about 35 different species of raptors, including owls, but they are non-releasable residents. I notice you are visiting in late April or early May - the Open House at OWL takes place on the 1st weekend in May each year, so that is well worth going to. Website: https://www.owlrehab.org/
Those are my favourite birding places; I hope others will add theirs.
As for wild owls, unless you are planning on being out at night or at least dawn/dusk they are less reliable at that time of year.
I hope you have a wonderful trip here; you are coming at a beautiful time of year. We are blessed to live in an area with so much wildlife and spectacular natural scenery.
Someone else will have to fill you in about Seattle; I haven’t been down there in many years.