My associate editor cannot contact the 2nd reviewer I submitted a paper to an IEEE transactions journal in March. The paper was sent to the editor, then the editor found an associate editor (AE), then the AE found three proper reviewers (but I do not know the reviewers). 

At the begining of July, I received the decision for the AE: the 1st and 3rd reviewers gave me Accepted with minor revision, the 2nd reviewer gave Major revision. So the AE decided it to be Major revision. I made some point-to-point revisions regarding the comments and resubmitted the paper.

Now, four months passed, I have not received feedback yet. A month ago I sent an email to the AE to ask for the reasons. The AE said that he cannot contact the 2nd reviewer. So what I can do now?

Can I suggest to the AE that he should make a decision based on the 1st and 3rd reviewers' recommendation? because the 2nd reviewer already gave me Minor revision in the first round peer-review, it seems that he would not have big questions.

Thanks.
You cannot suggest the editor do something - the editor doesn't need your advice on how to do his or her job. What you can do is ask for a decision. Say something like, "it's been four months since I submitted this revision. When can I expect a decision?" The aim isn't to get the AE to make a decision, but rather to look at your paper and its status. The AE should understand that four months is a long time to wait, and that he or she should decide what to do next instead of continue to wait for reviewer #2.

As for probable outcomes, there's a good chance you might have to wait longer. From your description, reviewer #2 was the one that suggested major revisions, which is why the AE is particularly concerned about hearing back from reviewer #2. If the AE is unable to contact the reviewer, then the most likely decisions are 1) accept or 2) invite more reviewers. If the AE trusts reviewers 1 &amp; 3, (s)he is more likely to pick option 1; otherwise option 2 might be the choice and you might have to wait another 4+ weeks.