The OnePay license allows for a single-return EFILE and printing. It also gives access to Québec forms for NetFile and printing of a single return. A OnePay license is required if filing a Québec return and a Québec license isn't present, even if a federal license is. EFILE and NetFile credentials still need to be obtained by CRA and Revenu Québec, respectively. You will be able to ReFILE your returns with the OnePay license, as long as you EFILED with the same OnePay license.
OnePay is limited to a single individual, corporate or trust return to a single fiscal year. Preparers seeking to do several years worth of returns, even for the same taxpayer, need to purchase a OnePay for each year. Depending on your situation, purchasing a full ProFile license may be of better value.
Please note that coupled returns and returns using family linking require a OnePay license for each individual.