Taken from the Canadian Gov. Website:
Dominican Republic Travel Advice and Advisories | Government of Canada
Hope this clears it up but having said that I have many times traveled direct from Toronto and not been asked for a return ticket. Can't remember when I've transferred from Miami but am doing that in April so I'll see if they ask.
4. ENTRY/EXIT REQUIREMENTS
It is the sole prerogative of each country or region to determine who is allowed to enter. All countries or regions have special requirements for persons intending to reside for extended periods (usually more than 90 days) or who plan to work, study, or engage in non-tourist activities. To obtain information on specific entry requirements, contact the nearest diplomatic or consular office of the destination(s) to be visited. Violations of entry and exit requirements may result in serious penalties.
The following information on entry and exit requirements has been confirmed with the authorities of the Dominican Republic. However, these requirements are subject to change at any time. It is the traveller's responsibility to check with the Embassy of the Dominican Republic or its consulates for up-to-date information.
Since January 23, 2007, all Canadian citizens transiting the United States when travelling to and from the Dominican Republic by air must comply with entry requirements to the U.S. For more detailed information, please see the Canada Border Services Agency (CBSA) web site
It is strongly recommended that all Canadians be in possession of a valid Canadian passport while abroad. A Canadian passport is the only reliable and universally accepted travel and identification document available to Canadians for the purpose of international travel. Starting April 30, 2012, Canadians will be required to present a passport to visit the Dominican Republic, which will need to be valid for the length of their stay. Until then, Canadians entering the Dominican Republic by direct air travel are only required to be in possession of valid official photo identification (such as a driver's licence) and proof of citizenship (such as a birth certificate). Canadian tourists must also be in possession of a return airline ticket.
However, Canadian citizens returning to Canada who present other documents, such as a Certificate of Canadian Citizenship, birth certificate, provincial driver?s licence, or foreign passport, instead of a Canadian passport, may face delays or be denied boarding by transport companies.
Canadians entering the Dominican Republic for tourist purposes must purchase a tourist card, at a cost of $10 US, which is valid for 30 days. Those wishing to stay for a longer period must pay a surcharge at the airport upon departure or request an extension by visiting the Department of Immigration in Santo Domingo. Those wishing to work in the Dominican Republic must apply for a business visa. More information can be obtained by contacting the Embassy of the Dominican Republic in Ottawa.
Foreigners may gain the right to reside in the Dominican Republic by acquiring a residence visa from the Foreign Relations Ministry and a temporary or permanent residence card from the Immigration Department. A student visa is also required. For additional information, please contact the Embassy of the Dominican Republic in Ottawa or its consulates in Canada.
Tourist Visa or Tourist Card: Required
Business Visa: Required
Student Visa: Required
A departure tax of US$20 is charged for stays of up to two weeks. The departure tax for stays longer than two weeks varies depending on length of stay and nationality. The tax applies to all international flights, and may be included in the price of the airline ticket. Travellers should confirm this information with their travel agents.
Selling, altering, or allowing another person to use your passport is a criminal offence. It could lead to the laying of charges and imprisonment if convicted. It could also lead to the denial of future passport services.
Special and diplomatic passport holders should verify all visa requirements for this and other destinations, as they may differ from those that apply to regular passport holders.
Although same-sex marriages are legal in Canada, many countries or regions do not recognize them. Attempting to enter as a same-sex married couple may result in refusal by local officials. For more information, contact the foreign government office accredited to Canada.