You don't have to buy an all-in-one seat, as they tend to be bigger/bulkier. You can buy a dedicated rear facing, then move the a convertible front facing. That is what we did and never had any problems.
This is true, so if that is an option for OP then sure. Someone also mentioned the cx5 may be a done deal, so then absolutely looking at a diff seat should the Graco not fit would be best option.
But if he's sticking with Graco, I do feel it will fit. Probably. But I'm just not sure, as many convertibles have issues. I mentioned narrow seating isn't a problem, but I was too quick to say that. It can be, in terms of belt width. there are many factors.
Example- I tried to follow best practices with my Clek and place it in middle of bench in cx9. IMO it's a no go. Belt in middle position doesn't provide adequate width for secure install, and seat is too shallow so carseat has overhang. I'd never have guessed that would happen in a car the size of cx9, but there you go. Mine is now in outboard position. In my CRV, fits middle no issues. It's not a compact vs other vehicle sizes issue. It's a specific car issue. Some are just not friendly to car seats (see Subaru forester forums if you want to see angry parents)
It's not rocket sci, but I've seen things. Friends with wobbly installs, front facing to early, using latch beyond recommended weight. Hell, most think Latch is better than belt install, which is wrong. Many people make errors.
I knew nothing of all this, so I paid trained installers to show me. 2 diff guys, for 4 seats in total. One was great. The other was with one of biggest chains in toronto area, his install was crap. Had 3 inches of play. I had to hop in to fix in order to drive home. Even trained pros get this wrong.
So, although it's not rocket sci, I feel a lot of people believe that and thus take it too lightly. I don't mean you specifically, but I think many parents take more chances than I would. But...to each their own.