I participate in the Employee Stock Purchase Plan (ESPP) offered by my employer. The plan allows me to contribute a percentage of my salary and buy company stock at a discount twice a year. I always sell the shares purchased under the ESPP plan immediately and use the proceeds to contribute to our RRSPs. Since our company stock is listed on the NASDAQ, I would prefer to deposit US dollars directly into the RRSP and avoid the pesky currency conversion fees.
As none of the discount brokers provide the option of keeping cash in the RRSP in US dollars, any contribution to the RRSP in US dollars would automatically be converted into Canadian funds. One easy way to get around the restriction is to buy US-listed stocks in your taxable account first and as soon as the trade is settled, call your broker and contribute the stock you just bought in-kind into your RRSP. I have done this many times in the past buying VTI or EFA in an investment account and then contributing the stock in-kind to the self-directed RRSP account.
If you contribute stock in-kind into your RRSP, you should be aware of superficial-loss rules that apply. When you contribute in-kind to the RRSP, from an income tax perspective, you are deemed to have sold the stock at the current market value. If you made a profit, you should declare and pay income tax on the gains but capital losses are disallowed under the superficial loss rules. This is not a big issue because you are contributing a few days after buying but it is something to be aware of.