It looks like you may be a Mac user... Our TurboTax CD/download versions are just for Windows. We don't make a Mac version.
In our online version (which works great for Mac users), you pay per return. Depending on what editions you choose, you may find the online version of TurboTax more cost-effective than the cd/download version, because you can choose to prepare the 3 returns in different editions (i.e. they don't all have to be prepared using TurboTax Premier).
Compare our online editions here: https://turbotax.intuit.ca/personal-tax-software/online-tax-software.jsp