JOEL - That all depends on which state you are talking about. You should not limit him to women in Utah alone. I know a lot of nice single LDS women in California :-)
Oh, you meant the state of widowhood. Well assuming you both live a long life, marrying another widow might be the only choice either one of you is going to have.
But if that is not the case I would hope that the current wife would have enough love and trust in her husband to let him pick someone(divorced, single, or widowed) that he can happily spend the rest of his life with. And likewise the surviving husband would have enough class and respect for his deceased wife to pick someone she would approve of (probably a widow).
There's no church doctrine that covers the propriety of who the survivor should marry. There's no harm in voicing your desires on the matter, but in my opinion, if a couple loves and trusts each other enough the whole thing is a non-issue and no promises need to be made. But then of course my wife already has someone picked out for me in case she goes first. :-)

SHERRY - In Genesis 22:12 why does the angel refer to Isaac as Abraham's "son, thine only son"? Are latter wives in plural marriages subject to the first wife, as when Sarah cast out Hagar?

JOEL - In Hebrews, Paul said:

"By faith Abraham, when he was tried, offered up Isaac: and he that had received the promises offered up his only begotten son," (Heb 11:17)

Even though Abraham had a son(Ishmael by Hagar) before Isaac was born, it was Isaac that God established His covenant with, and as such could be called Abraham's only "begotton son", being a similitude of the Father's only begotton son Jesus Christ.

"But my covenant will I establish with Isaac, which Sarah shall bear unto thee at this set time in the next year." (Gen. 17: 21)

Besides this, at the time Abraham was told to sacrifice Isaac, Hagar and Ishmael may not have been living with Abraham, so Issac may have been the only son Abraham had living with him.

SHERRY - How can the scriptures say "Therefore shall man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh" and "Thou shalt love thy wife with all they heart and shall cleave unto her and none else" be applied in plural marriages?

JOEL - Notice those scriptures say he should "cleave unto his wife". Be it one wife or three wives, as long as in God's eyes each one is his "wife", they are not violating these commandments. God said these things with the intent of commanding against any adulterous relationship a man might want to have with someone he is not married to. So technically this would not apply to polygamy. In the D&C God refers to this scripture just before He talks about adultery (D&C 42: 22-25). Jesus did the same in the New Testament (Matt 19: 5-9).