I wrote the exam end of April and just got my mark today and passed a couple SDs above the mean. I am a pretty avg CMG. To other CMGs reading this... I didn't find it overly difficult. I mean there's a lot where you're not 100% sure but most of the questions are geared towards a family medicine level of knowledge about things. I wasn't tight on time for the MC (had 30 min left at the end to review) like others have said but I'm usually in the top 5-10% of my class in terms of exam writing speed so I expected not to run out of time. The written portion has a ridiculous amount of time alotted like I finished with an extra 2 hours or 1.5 hrs. Some of the questions were weird and read my mind.
For the IMGs... I could see there being a lot of tricky questions that would be gimmes to a CMG. I had a stupid amount of questions on ethics specific to Canadian laws, Canadian organizations (ie. If you had an ethical question who would you ask for definitive advice... Your local college of physicians and surgeons, your program director, the CMPA, the CMA, etc). Like those are tough to study for its things you just pick up along the way really. Maybe Toronto notes sections on organization, ethics, legal, etc would be helpful.
To the question about writing at the end of 3rd year... Most of what I drew upon was previous clinical experience from third year. If you have finished all your core rotations I would seriously consider it. Some people feel more comfortable having "sit down" time to study and review, though. There's no wrong answer.