I would like to know if its a good idea or even possible to get my spouse's biometrics done before hand and submit it with PR application for spousal sponsorship category.
If your spouse applied to come to Canada for another reason (visitor visa for example) and already gave their biometrics, they should accept that since biometrics are good for 10 years. But as mentioned, we had this done with a BIL letter from a previous attempt to come to Canada.
Before sending my wife's PR application, we had applied for her to have a visitor visa 2 years ago. I mentioned that in a letter and included that UCI number. When we linked our application to the GCKey account, they appear to have accepted that.
If this is your spouses first attempt ever to come to Canada, then you must wait for that BIL letter.