There are 2 places in Vancouver that are GREAT for coffee and a sit down.
The first I will recommend is Tim Houton's Coffee which is one of the main chains of coffee shops in Canada.
Ask for a Large Double Double and a Canadian Maple Donought. These are truely THE BEST coffee's you can get in Vancouver.
The next place I would recommend is Starbucks on the corner of Granville and Smithe in Downtown Vancouver. The address for the store is 900 Granville.
I worked there as a supervisor for 5 months, and I loved it. There is WiFi access, and the selection of coffee and food is some of the best in the area.
If Rob or Sandra are working there, they make the most AMAZING coffee. And I would recommend a Caramel Macciatto if Rob is making it (he does the best) and Sandra is great all around.
You can sit and people watch, go to one of the 2 cinemas over the street, or one of the 2 comedy clubs or concert halls over the street too.
There is a great bar next door, the BEST pizza place in Vancouver on the other side of it, and all in all a great atmosphere.