Edmonton is a newish airport, and as per the website - plenty of places to eat and drink. That shouldn't be a problem.
I'm not sure what the International -> Domestic connections system is like but it generally goes like this
1) Canadian Immigration
2) collect bags (which if you are on WestJet for both flights will probably have been tagged through to Kelowna - but you still have to collect them for Customs purposes **)
3) Canadian Customs - you hand over your arrival form and walk though. Unless there is an issue then the Customs officer will call you over for a chat and a little search (unlikely)
4) Deposit your bags at the dedicated Westjet counter/baggage belt
5) proceed to your departure gate.
** at some of the bigger Canadian airports you don't have to physically collect your bags, but EIA doesn't seem to be one of these. So I am assuming this is the procedure still. The website is not clear on this.
4 hours is a reasonable amount of time if your flight from LGW is on time, and the CBSA is well staffed. You won't be rushed, but will still have time for some refreshment and a walk around.