OK, so a mid to high end component set is right for you, but the real issue is sizing. I'm assuming here that you want the same position on the tandem as you have on the Cannondale.

In a nutshell the relative position of the bottom bracket, seat and bars are what matters, so you need to check that first the bike is long enough, then whether it's the right height. First check is to do a back of the envelope calculation, but to do it properly you should really do a scale drawing of your single bike position then overlay it on a similar drawing of the frame you are considering.

Step 1: Cockpit length
To compare frames all you should also adjust the top tube length for any difference in the seat tube angle. But since the T2000s both share the same seat tube angle, no correction is needed.

The T2000 Cannondale touring bike in 63cm has a top tube of 59.7cm with seat tube angle 72.5 degrees. The large T2000 tandem has a top tube is 57.5cm with seat tube angle 72.5 degrees. This means you'd need a 2cm longer stem on the tandem to get the same reach.

In my opinion having a long stem on the tandem matters much less than on a single bike because weight distribution isn'd changed as much. Problem will be if you're already on a 14cm stem that 16cm stems simply don't exist. What stem do you use at the moment on the Cannondale?

Step 2: Bar height / standover
The idea is to get a frame size that uses a reasonable number of spacers (in my view less than 2cm ideally, never more than 4cm) to set the stem and bar height and also get a bike you can straddle. The Trek has a 14.5cm head tube, and fork which uses a long drop brake caliper I think. Measure your cannondale's head tube and see how it compares, then adjust if the fork height is different (most likely similar or slightly longer as it's a tourer not a road racing bike). You will need to make up any difference with spacers or an angled stem. I'd guess (as the cannondale geometry doesn't list head tube length) that you would need more spacers on the tandem as the T2000 probably has a longer head tube than the Trek. That means that if you're running 2cm of spacers on the T2000 you will struggle to get the bars high enough.

Summary:
My hunch is that the T2000 is about 2cm smaller than a custom-sized bike would be, but it may be possible to get it to fit you, particularly if your position is on the short and low side.

Next steps:
Your homework - check what you would need to do to fit the Trek and Cannondale. Then call your favourite shops and see whether you can get test rides. If so, tell them your and your stoker's measurements and the stem length, # spacers you think you need. They should then be able to set up the bikes for you to test ride. I think it will come down to whether you like the Cannondales' fit, stronger brake system but worse componentry versus probably a worse fit and better components on the Trek. If you like the Trek components but can't fit either, then I'm afraid more money and a custom Co-Mo Calfee or simliar is the answer.