Do you think your driving will be mostly urban, suburban, or highway?
For maximum mpg and a decent rear seat, there's the Toyota Prius.
For a larger rear seat, maybe the Toyota Camry Hybrid or Ford Fusion Hybrid.
I checked autotrader.ca to make sure cars were available within your parameters.
Crossovers have only recently become capable of better than 10/100km in real-world driving, so these (such as the Mazda CX-5) are probably too new to fall within your budget.
One hatchback that could be a good fit is the Hyundai Elantra Touring, but it's fuel economy won't come close to that of the suggested hybrids. Perhaps around 10 liters / 100 km. But it has a very roomy rear seat for a compact hatch.