There has been a great deal of change in the Canadian markets recently. The TV Fool database is being edited but the work is still in progress. The result is that I have to assume many analog stations shown on your TVFR are no longer on the air and many digital stations shown as pending may already be live.
To answer your question of 8 vs. 4, I'd opt for the 8-bay antenna if that were the only available choice. The only US stations available to you are KVOS and KBCB which are broadcast from Mt. Constitution on Orcas Island. There is no reasonable hope of seeing the Seattle stations from the location used for your TVFR.
To be on the safe side, I would suggest you check with the forum at
http://www.digitalhome.ca/forum/ I think you may want to consider an all channel antenna option, not just UHF. A bit more research would help you understand if there will be stations of interest on one or more VHF channels in your area.