Hello,
It's alryt to defer your term. Though you must have deferral letter from college/uni as it will be required at POE. changing college/uni or level of study from PG to Masters or Masters to PG doesn't impact anything on your file at all.
http://www.cic.gc.ca/english/helpcentre/answer.asp?q=487&t=15
Post-secondary student
You may change your school, program and/or field of study without applying for a new study permit. You do not need to apply for a change to the condition of your study permit, either. You may continue to use your study permit as long as it is valid.
If you are changing your level of study (e.g., bachelor’s to master’s), you do not need to apply for a change to the condition of your study permit, either.
Now, extending your study permit, well You haven't been issued a study permit yet as it will be issued at POE when you Land for the first time. With the deferral letter, you can show the IO, and he/she will issue you study permit accordingly. Now, TRV, TRV should also be changed (however, I won't suggest to do that, if you do it from the country you are in, it may be of little hassle, so once you land here and get your study permit, continue with that). And get new TRV issued only when you need to travel outside Canada.
For example, if you start your session on 1st Jan 2014 and study ends on 1st Jan 2016 - you have study permit till end of 1st jan 2016 but TRV ending on 1st June 2015. In this situation, you really needn't worry about TRV unless you need to travel out of Canada.
Hope it clarifies all your concerns for you.
Cheers!
