McGill University has a great collection of Canadian war posters online.
The holdings of the Print Collection in the Rare Books and Special Collections Division include some 250 Canadian posters from the two World Wars. The posters are accessible to researchers who visit the Division's Lande Reading Room; a printed finding aid is available from the Reading Room Supervisor.
This website contains basic descriptions and images of each poster, an artist index, a search facility, and an essay about Canadian War Posters. The search facility enables you to search by World War, by Category, by Artist, or by keyword. The results of your search are displayed as thumbnail images. Click on a thumbnail to obtain a larger image and a full description. Each description includes the following information: the poster ID number and title or lead text; the date, artist, and publisher, when known; size, and appropriate notes.
I dig this sort of thing. Here's one of my favourites from WWI.