Surgery involving the Prostate Gland will always cause erectile dysfunction, and sometimes, urinary incontinence and bowel problems.
When you have had the devastating diagnosis of Prostate Cancer you will be given some choices such as Watch and wait (Active Surveillance) if the tumour is within the capsule and has a low Gleeson score (this is a method Doctors use to measure how aggressive/ dangerous the tumour is). If the score is high then active treatment will be needed.
The active treatment will usually involve Radiotherapy or Surgery. There are different treatments with Radiation and these should be discussed with your Radiologist.
Surgery can be open, laparoscopic and robotic. The skill of your surgeon is what matters most. Bare in mind most experienced Urologists may have done many hundreds of open surgeries but very few robotics, as it is a new technique and involves very expensive machines.
The evidence is not there yet that robotic or laparoscopic techniques are better than open surgery.
You need to ask your surgeon questions before surgery about the above. Second opinions are good although most Surgeons will lean toward surgery and most Radiologists will lean toward radiotherapy.
A frank discussion with your GP or a specialist nurse may be useful as they will have seen many men who have undergone different techniques and be able to give an unbiased opinion