I have simple choice North America plan and it says talk, text and data up to 5GB is included. When travelling to Canada - do you need to turn on Data Roaming on your device?

Yes, you do.  You are still roaming on to another carriers network for service when in Canada.  Usually Bell/Telus.

Can I watch my YouTube TV while traveling in Canada? If so, is there a limited amount I can watch? 

wjvmstutz wrote:

Can I watch my YouTube TV while traveling in Canada? If so, is there a limited amount I can watch? 

Depending on your plan.  You might have 5GB of high speed data in Canada.  That will go very fast watching live TV.