I want to put the 2.7crt tanzanite gemstone on a necklace, one to give to my girlfriend as an anniversary gift and two as an investment of course. I was thinking a nice but simple 18k white gold necklace. I want it to be elegant but nothing over the top. I was wondering if you could give me an estimate of what the price would be for a necklace of this sort and if you can recommend any specific jeweler. Thanks

I trust it's good quality. I know a little bit about Tanzanite and less than 2% is excellent quality or better. I'd make sure it's been appraised before you spend money on a setting and chain.

You are giving it to your girlfriend as an investment?

And there's a great jeweler on Bloor Street in Toronto.

First tip is to be very careful. Tanzanite is extremely fragile, probably more so than emerald. It will chip very easily. It might even be a good idea to get the stone appraised beforehand and insure it in case of a mishap.
I am not sure if a jeweler would guarantee the stone against breakage while it is being set. It is that fragile, be sure to discuss this with the person taking the work.
I would also recommend a prong setting, rather than a bezel setting. Setting the bezel can put some pressure on the stone, whereas prong setting will put much less.
Last is to be careful with the finished piece. "Wear it like a good suit", on occasion and certainly not while you out gardening.