Usually PBs install mastic in joints like that and then apply granules while it's still wet. The granules help it to blend into the decking color/ texture. I'm not sure if there is a max width for mastic, an inch is a pretty big joint!

Thanks. Is applying mastic a simple job? Is there a specific product you can recommend for a novice DIY'er?

The first row of pavers that go around the spa were glued/mortared to 3' wide poured concrete that goes around the entire pool, so stability of the paver isn't really the issue here. Just looking for something to fill the space.

I think it wouldn't be a difficult DIY project. It's a self-leveling compound, so all you need to do is blow the old sand out of the joint, make sure the mating surfaces are good and clean, then pour in the mastic. Deck-O-Seal is one of the products I've seen for sale on various pool sites, manufacturer's link is below.

Here is a link that might be useful: http://www.deckoseal.com/system.htm

I contacted dealoseal directly and was told there are no distributers in my area (Toronto, Ontario). Any other products anyone can recommend to fill the space between my pavers and the hot tub/spa?

Do not use deckoseal, too hard to work with