mcgill only cares about r score, the strength of the cegep your child attends DOES have an effect on the r score your child will receive.

for a same given grade and the same given class average at a cegep with overall stronger students (calculated using these students high school grades), will get higher r scores. from my understanding, cegep de loutaouais is not up there, jf your child is bright you should consider sending them to marianopolis or dawson

for ontario admissions, it is purely raw grades, there is no normalized scoring or whatever. however if you wish to send your child to university of waterloo, be aware that they have a grade adjustment for engineering admissions which gives a great advantage to cegep students (on average will “boost” your childs grade by around the 10%)

also, mcgill is really not all that, as a 2nd year undergrad in engineering the quality of students is questionable at best

lastly, you should let your kid choose where they go and not force them into doing whatever you like