For the LMIA, it doesn't make a difference if the applicant is in Canada or not. For the work permit, lower chances of approval if the applicant is in Canada since IRCC likes the applicant to be able to show ties to their home country and this is obviously more difficult to do if they are already in Canada.
For your second question, it depends on the province and google is your friend. Google: 'becoming a certified engineer in <insert province name>'