Hi,
Well this is my personal opinion. I may not be correct.
If you apply for Immigration on grounds that your father's health - then you can get into trouble - as they may ask for more details - means more trouble for you.
When I got here, they suspected that I have a problem because they thought found something on the X-ray. And I had to do a re-Xray which delayed my Work-Permit by a couple of months.
If you are the only son - then you may bring them here and then apply for the Imm in US. And till the time, they don't get their Imm papers - keep on extending the stay on Visitor Visa, on grounds that there is noone to take care of them.
This worked for someone who got her Mother's Imm - but it took a long 2 years thru Buffalo. They applied around 2001. It took more time - but atleast her mother was here throughout the process. Also, mind you that she could not leave Canada till she finally got her papers.
My mother's Imm sponsorhip papers were received at Missisuaga around July 2004. They haven't yet send them to Delhi. They are currently processing for Oct 2003. So, you can imagine the delay.
Best of Luck