You can get custom trade advice for your synced leagues.
If you haven't synced your team yet, do that first.
Go to the In-Season navigation, and then click on Custom Advice. Below the league you want to evaluate, click Trade Analyzer. That will take you to a page where you can see customized trade advice for your team.
Your team will be loaded automatically on the left side of the page. On the top right of the page, select the opponent's team you want to trade with. It will then display their full roster on the right.
Check the boxes next to the players you intend to trade, it the trade analyzer will show the trade value on each side of the trade.