My spouse has just told me that he/she wants a divorce. Can I oppose the divorce?
Basically, no. In the United States and Canada, you cannot prevent your spouse from divorcing you. A divorce will be granted whether or not you agree to it, whether you participate in the legal proceedings or not.
In most of the United States, "No Fault" divorce is the standard. Under "No Fault", your spouse may choose unilaterally to divorce you at any time without having to give any specific reason.
Many jurisdictions now in fact do not accept anything other than "irreconcilable differences" as the reason for seeking a divorce.