We are planning this:
1day-Arriving 20May in Vancouver from Toronto, rent a car on international airport and go to downtown Vancouver for sleeping. Around Robson street.
2day-Take a ferry on Tsawwassen to Victoria , visit Buchart Garden , sleeping in Victoria around Inner harbor.
3day-Whale watching -Prince of Whales after go to Royal British museum.
4day-Victoria to Nanaimo , ferry to Horseshoe bay - Squamish -Whistler - afternoon go back to Vancouver.
5day-Visit to Capilano bridge and Grouse montain.
6day-Visit Stanley park and shopping Robson street , Gastow
7day- Walking downtown
8day-Fly to Calgary
How difficult is to park a car on downtown Vancouver ? Parking downtown are expensive ?
How about this planning ?

I think Day 4 is highly undesirable. You'll be driving all day, and not seeing anything (except when on the ferry).

I would take your time on Vancouver Island, and get back to Vancouver late that day. Use Day 5, 6, or 7 to go up to Whistler.

Topping for Suzybr. Don't know why even after I replied, it still shows "0 replies" yesterday...

if you want to go to whistler on day 4, i'd plan on getting a room up there and head back to vancouver the next day. otherwise it may be too busy.

Day 4 - while not impossible would be extremely tight for time. Drive from Victoria to Nanaimo takes two hours, wait for ferry - unknown time, ferry to Horshoe Bay another two hours, drive to Whistler two to three hours. Did you actually want to spend any time in Whistler? I think you need to do as another poster suggested and stay overnight in Whistler to get the most out of your experience.

Parking in Downtown Vancouver can be quite expensive (although, it is dependent on the time of day). The City of Vancouver recently increased the rates for metered parking. However, after a certain time in the evening (I believe it is 8:00pm) the meters are no longer in effect, and vehicles may park for free in those spots. The alternative to street parking are parkades, which offer flat rates for a full day's worth of parking. You may have to do a bit of driving around in order to find the best parkade rate deals.

If you park on the street in Vancouver, read the signs very carefully. If it says parking until 8am, then you better drive away by 7:59, because I believe Vancouver has the most efficient car-towers in the world. And don't even think about parking at "resident-only" spaces unless you have a permit.

1day-Arriving 20May in Vancouver from Toronto, rent a car on international airport and go to downtown Vancouver for sleeping. Around Robson street.
2day-Take a ferry on Tsawwassen to Victoria , visit Buchart Garden , sleeping in Victoria around Inner harbor.
3day-Whale watching -Prince of Whales after go to Royal British museum.
4day-Victoria to Nanaimo , ferry to Horseshoe bay - Squamish -Whistler - sleeping in Whistler.
5day-Morning go to visit to Capilano bridge and Grouse montain, sleeping in North Vancouver.
6day-Visit Stanley park and shopping Robson street , Gastow
7day- Walking downtown
8day-Fly to Calgary
Victoria -Nanaimo: is it worth ? Or return to Vancouver is better ?

In my opinion, it might be best to eliminate Nanaimo from the itinerary. Unless there is something in particular that you wish to see or visit in Nanaimo??? Instead, I would return to Vancouver on Day 3 by catching one of the late ferry sailings. Then, on Day 4 you could do an entire day trip to Whistler. Hope this helps!

P.s. The Capilano Bridge is a bit of a mundane tourist attraction, I have to say. It doesn't really have much of a wow! factor. An alternative could be a visit to the Lonsdale Quay Market where you can get a view of Downtown Vancouver from the other side of the Burrard Inlet.