1. Can I file tax return in Canada, if yes which category? My total stay in canada for current year will be five months.
Yes, file as a resident of Ontario.
2. In TD1 fedral form I see that there is provision of Tax rebate for first 10527k also another 10527 for your dependent Spouse Will I get that rebate in Tax retrun.
It is prorated. You will get $4,386 (10.527*5/12) and can claim this for your spouse as well. You can also claim the ON personal amount prorated for 5/12 months. You wont get a refund of all your CPP contributions, or EI, but you will be entitled to a (very) small pension at 65.
3. Can I also claim tax rebate on Rent paid during my stay which is 5000 (1K per month)
No.
4. Is deductions made by empolyer justified ? I have given both TD1 form (Fedral and ontario) to them.
It seems a bit on the high side but it will be corrected when you file your tax return.
5. Can I complain with some Govt Agencies if Empolyer is not deducting taxes properly. If yes please let me know
There are mechanisms for doing so but it really does not seem worth the effort.