I thought I would post this for anyone else thinking of doing submerged centerpieces. I tried a lot of ideas but this one worked. 
I bought 5oz fishing weights - like these: http://www.amazon.ca/Bullet-Weights-Bank-Sinkers-3Oz-Card/dp/B000676X6W/ref=sr_1_55?s=sports&ie=UTF8&qid=1434310020&sr=1-55&keywords=fishing weight
Tied them to the rose stem with clear fishing line, dropped in, then dropped in rocks to cover the weight with.
You can see my fishing line in this photo cuz I just wanted to see if it worked, wasn't really going for looks. Also I will be adding a floating candle on the top like my inspiration image...
I will be setting up all the centerpieces the night before the wedding, tying on the weights and putting in vases. Although will only fill about 1/3 with water for easy transport to the venue.
For any Canadian brides, the cheapest place to buy these weights is Wholesale Sports or Army&Navy! ;
