I'm with the 5 year FRCPC program, so I am not the best person to chat about GPA lifestyle or job market. Couple things I thought about though:
As far as I know in Western Canada, FRCPC trained anesthesiologists are close to the only trainees being hired on these days in major cities. There are lots of jobs for GPAs in great rural areas all over the country, and some medium sized locations. Doing a couple locums post residency to find the right fit has been a common pathway from some of my GPA pals, while others have already been an established GP in a certain town and have been asked to do the GPA training with a job on return. So all that to say, I would think you'd need to be comfortable living in a rural location as a GPA and should consider if that will work for your lifestyle/family/interests. This is a big consideration for lots of people.
From an anesthesia perspective, the GPA vs FRCPC cases are quite different if you consider subspecialties of anesthesia (ie cardiac, thoracics, neuro/spine, transplant, major trauma, vascular) to the average rural anesthesia case, but it's really not so different if you consider that a lot of your time as a non-subspecialist staff anesthesiologist will be doing bread and butter sedations and GAs no matter where you work. My advice would be to think hard about what will keep you fulfilled in your career in the long run. Like you mentioned, smaller centres will refer out their complex patients, so if you're someone who enjoys the more complex periop management of anesthesia then FRCPC affords more opportunities to explore that. For some of my colleagues, the challenge of approaching a complex case or acute resuscitation is what keeps them interested and fulfilled. However, some may find that as a FRCPC practitioner the novelty of looking after complex patients and doing complex cases will wear off with time and experience. The more cases you do the more routine it becomes, especially after you've been well trained for 5 years and given that you'll be working in larger hospitals with the support to manage complex periop surgical care. As either a FRCPC anesthesiologist or a GPA there will be cases that are challenging for you. Anesthesia in a rural setting is incredibly complex when faced with an acute presentation in a setting with limited hospital and staffing resources and considerations for transport/referral.
In terms of working in ED/clinic as a GPA - I can't speak to this in detail. Some of my GP colleagues have gone on to just do GP anesthesia, and others have accepted jobs with time spent in ED or clinic or both. The variety and balance is certainly what many of my GPA colleagues have loved about their job. To me this seems like a wonderful option. Doing just anesthesiology means that you have less of other aspects of medical practice - things like patient continuity, history taking/diagnostics, and admitting/being MRP. Many of my colleagues don't find they miss these aspects of care as anesthesia alone affords a greater degree of flexibility with call/time-off/overhead, but for some people balancing out an anesthesia practice with time in clinic/other areas is a real value-add to their career.
I'm sure there are other factors that other people have considered important. My decision was based on not being interested in the FM training program, wanting the option of living in a major city and/or doing a subspecialty, and loving resuscitation/trauma medicine. However, as a medical student I didn't appreciate that things I thought were really exciting as a medical student are not as exciting after a couple years, and rather that it's the other aspects of my career - like patient-physician relationships and a sense of community in my workplace that keep me happy and excited to come to work.