I don't agree that it needs huge money to speculate in currency fluctuations. It's like any other investment -- the more money you put up, the more your potential return.
To invest in a currency, you really only need to invest in something that is valued in a currency that you expect to increase in value. For example, if you use US$ to buy a Canada Savings Bond worth $1000 CAD, and then the C$ increases 10% relative to the US$ over the term of your bond, you've made 10% in addition to the interest rate on the bond, provided you cash out the bond in US$.
So, you can really buy anything valued in C$, like a house in Canada, a Canada Savings Bond, or a stock of a Canadian company. If you want to speculate on currency only (ie., currency fluctuation will be the only factor in your investment that varies) you should get a fixed-income investment like a Canada Savings Bond or a GIC. If you buy a house or a Canadian stock, your return will be based on both the appreciation or depreciation of the underlying investment, as well as currency.
As for your tax situation, sorry I don't know anything about US tax laws, but in Canada you would declare any money made or lost on currency fluctuation as a capital gain (or loss), and it would then be taxed at a more favourable rate than interest income or employment income.