You're likely going to encounter a lot of snow on the higher elevation trails in May. Anything in Garbaldi Park, Golden Ears, Howe Sound Crest Trail etc is likely to have quite a bit of snow. The HSCT is awesome but we were still hitting snow in late August last year and there is some sketchy terrain, so I'd be hesitant to do it in May unless I was well prepared for snow travel.
I would likely look at hiking trails that travel along the coast, rather than ones through the mountains. The most notable ones are the Juan de Fuca, West Coast Trail, North Coast Trail and Sunshine Coast Trail. All of these should be snow free. Of these, I would recommend doing the Juan de Fuca because logistically it is much easier than the WCT, it's radically cheaper and you can hike only as much as you want. I personally would suggest leaving a car at Sombrio beach and then hitching hiking about 30km to the southern terminus. That might not sound like much distance for 3 days, but the terrain is fairly rugged and the camp sites are amazing so you want time to enjoy them. Spend day one getting to Sombrio, hitch hiking back to the start and then hiking a couple miles to Mystic Beach. Then camp at Bear Beach night 2 and Chin Beach night 3 and then exit the following day. If you're a fast hiker and you don't have 4 days/3 nights then you could probably lump two days into one but it would be a long day. There aren't a lot of campsites so you pretty much need to camp at these beaches.