Hello. I'm visiting friends for 3 weeks on the 14th January. I have a return ticket booked. There is a chance I may decide to stay longer (my friend is having a baby and it would be nice to be there for the birth) in which case I would put my flight back. I'm from the u.k and I'm aware we are allowed to enter Canada for 6 months. On initial entry when asked how long I intend to stay for, if my response is 3 weeks, my initial plan, is this the amount of time stamped in my passport or will it be the 6 month stamp?
Typically they just stamp your passport with the entry date which gives you a default six month visit. It's rare they limit your trip to a specific number of days / weeks (although it does happen).
