The Matrix is just about the same size as the Mazda3 hatch, not the Mazda5. Plus it only has two rows of seats and is built overwhelmingly in front wheel drive. The awd version is pretty rare.

I'd say that the closest vehicle to the FR-V is the Mazda5 although the FR-V has regular doors as opposed to the 5's sliding doors. If anything I think Honda would wait to see how the 5 does before bringing the FR-V over. Honda is not really known to charge into emerging market segments (notwithstanding the notable exception of hybrid electric cars).