Welcome, Little Red Micra!
You're not far away - I'm just down the river in Brockville. Practically in the neighbourhood.
I'm sure you've noticed this forum is fairly quiet these days. There was a lots of excitement when Nissan re-introduced the Micra to the Canadian market 5 years ago. That has died off some. (Also, the Quebecois contingent is now congregating on a mainly French language site elsewhere, tabernac!)
One way to let the rear seatbacks fold flatter is to remove the lower seat cushion. Happily, it comes out without tools:
Thread: DIY: Turning your Micra into a micro cargo van... rear seat removal
Sadly, you're somewhat of out of luck as far as the front seat goes. The ideal thing would be to remove it (4 bolts), if it weren't for the fact it has an integrated airbag, and turning the ignition on with while that airbag is removed will set a fault in the computer. (May even disable the remaining airbags - I'm not 100% on that issue.)
One way around this is to set up some kind of light, removable platform as I've seen done with a similar sized car (with the same airbag-in-seat issue), the Mitsubishi Mirage. Check this owner's approach, leaving the front seat in place, but reclined all the way:
The plastic is from cheap modular shelving. Or you could DIY something with light plywood.
Glad to have you here!