That being said, it is not always possible. In some cases there are postings that will not facilitate both your Trades.
Another factor is Rank. Normally at the JrNCO level there is not a problem, but as you progress through your careers, there may not be positions for two WO/MWO/CWO at the same Base in your different Trades. The same will go for Offr Ranks, at times.
Your Trades play another role. If per chance you are Infantry and she is an RMS Clerk, then you will be limited to postings to Bases that have Infantry positions only, while she could be posted to any Base or Embassy that the CF has personnel.
Career Managers will try their best, but they can not always guarantee that both spouses in different Trades will be able to be posted to the same Base.