Thank you very much for reply in detail.
I have driven to Canada. So, my exit was by road. My I-94 card was not taken by Canadian Immigration and I did't had to go to US Immigration while I was exiting from US.
Not returning I-94 can cause me any problems in future ?
----YES, how do they know you left US?
How can I return my I-94 card to USCIS now ?
---------- send your I-94 to the below address and write the date details on cover letter that I-94 was not taken by Canada immigration and you went out of US on dateXYX ( keep the copy of letter with you, better send the letter with return recieptand keep the copy of your letter, the return reciept and copy of I-94 both the sides with you.
http://www.ccusa.com/pdf/INS Departure.pdf
Please help..
Thanks,
GS