I think the first year is the most different. Med-P is more like another year of cégep : you have very few obligatory courses and you can do anthropology, maths... things not related to medecine. The schedule is definitely not full : I saw one and you can make sure you only have 3 days of school (about 15-18h max).
The année prep at UdeM is more medecine intensive, in the sense that the classes are basic sciences tailored on the medical curriculum. And, you have about 25-26 hrs per semester.
So, in one, you have more like a liberal-arts education for one year, and for the other, you're like directly a foot in med school
Oh, and the Campus Mauricie at UdeM has gross anatomy on cadavers too Renovated anatomy lab and you have access to the plastinated members for studying for your 5 years At the Montréal Campus, you can come during the summer I think too!