I recently learned that the US dollar symbol ($) is of Spanish design - meaning 'peso', and was adopted to distance the US from Britain after independence. Why do other countries also use the $, specifically Canada, when their relationship with Britain never reached such a low?
One thing that's important to remember is how weird the British monetary system was back then (and up until 1971). 12 pence to a shilling, and 20 shillings to a pound. Part of the rationale behind using a nice round number like 100 was the same vogue of Enlightenment thinking that brought us the metric system and the failed French Revolutionary Calendar. The Founding Fathers, and Jefferson in particular, wanted a system of currency based on reason, and the dollar divided into 100 cents was born. People were slow to adapt to this, though, and even through the 1850s people were still pricing in shillings (with six shillings to a dollar), particularly in New England. Source
In the middle of the 19th century, Canada debated whether to use a system like Great Britain, or a decimal system like the US. They ultimately decided that a decimal system would be better, to match up with their neighbors to the south. The switch from the Canadian pound to the Canadian dollar occurred in 1858.
As to why the symbol itself took off, that I couldn't tell you. It was first used in 1768 and that's all I know.
not sure if you mean adoption of the symbol "$" for various currencies, or adoption of currencies named "dollar", but here are some previous posts to get you started:
How did the word dollar originate?
Why is the dollar sign $ an S with a line through it?
After the US dollar was created, how long did it take to take mass adoption?
Why did Australia and NZ (and Canada?) switch from Pounds to the Dollar back in the 50's / 60's?
When America adopted the dollar sign it became synonymous with decimalization. When other countries wanted to use decimalization, an easy way of basing the currency out of parts of 100, American had already been on decimalization so it came with the $.
The $ was in use as mentioned for peso, so the $ is not truly American but adopted for convenience as it was already used. The dollar sign was already in use and for simplicity it was not changed. It was not chosen only to separate itself from Britain, in the age of reason it was just thought better.
If you are really interested in the history of the Canadian dollar I found this book helpful.