Sorry, I wondered if all the ingredients would translate. I lived in Canada for 4 years,so you think that I would know!

Cordial is indeed sweet, flavoured syrup. You would normally add it to water for a sweet kids' drink.
Gastrolyte is a trade name for an electrolyte replacement drink usually used for people with gastroenteritis. You can buy it in chemists/drug strores in sachet form. It comes in different flavors, but I just buy plain so that I can add my own flavouring with the cordial. I just looked in the cupboard and the the sachets are 4.9g. and my husband must have got some freebies( he is a pediatric gastroenterologist- it is about the only freebies HE gets) of another brand- Hyralyte. I guess it works the same.

The polyjoule I also buy from the Chemist/ drug store. It comes in big tins and is quite expensive. People use it medically to add to sick kids feeds to add more calories.

One of the nice things about making your own gel is that you can make it as thick or thin as you like. I find it quite hard getting the commercial thicker ones down my throat especially when I am running.

I hope this helps.
Sue