I live in the US, and can only seem to find a variety of soda syrups that ship to Canada here.
https://www.sodacentre.com/collections/syrup
This was my best lead but am looking for sometime similar.
I wouldn’t add too much of flavors like this or it ends up tasting weird. You’ll learn to dial it in with experimentation. Each one is slightly different, but as a general rule five drops and swirling to mix is my first attempt.
If you want something to taste like a sugary drink, you’ll want a syrup designed for that. And there I’m afraid I can’t help you, because it isn’t my use case for the SodaStream.
By the way, make SURE to not add flavoring until after you’ve added the carbon dioxide. Otherwise you’ll end up with a mess. Trust me. 😅