My partner of many years has been diagnosed w/ prostate cancer. He has not started treatment yet, but does need cialis to maintain an erection. The problem is that he is not achieving orgasm.

I'm sorry to hear about his diagnosis. When you say he can't achieve orgasm, do you mean he cannot ejaculate? You might ask him if he has lost some of the sensitivity necessary to take him over the edge. Or if he has sensitivity and has feeling of orgasm only without ejaculating. If he does then it's possible he is having retrograde ejaculation where the prostate is not opening and the ejaculation goes backward into the bladder. He could tell by urinating after sex to see if semen is mixed with his urine.
He should tell his physician about the problem and have his testosterone and estrogen levels tested. If his testosterone is low that would cause a loss of sensitivity. However, they won't prescribe testosterone replacement therapy to someone with prostate cancer but at least you would know whether this is the source of the problem or not.

Myself, yes, they both enhance the power of orgasm. I find Viagra gives a harder erection (like rock) and enhances sensitivity because of the added blood flow to the sensitive nerve endings in the penis. Cialis erections are still hard but say 80-90% of what Viagra gives,I have a bigger orgasm with Cialis, the head of the penis is far more sensitive with it and the orgasm is unlike anything I have experienced.

Viagra gives rock hard erections and kicks in quicker in the 50mg or 100mg dose and lasts about 4hrs, longer if you don't have ED.

Cialis gives solid erections,it takes awhile to get going though, half hour to 2 hrs to work effectively the 20mg pill can last 24hrs or a bit more and for me provides more pleasure.

Both the above cost quite a lot, but they definitely work very well.