Canada is famous for many things, such as beautiful mountain landscapes, a disproportionate representation of funny people in Hollywood and having French as one of its two official languages.
The short answer to whether you need to speak French when you go to Quebec is, "No." Even though the majority of the province is francophone (French speaking), English is widely spoken in major cities, like Quebec City or Montreal and tourist havens like Mont-Tremblant and Tadoussac.
Even outside of the major metropolitan areas, employees at tourist attractions, like whale watching operations, hotels, and restaurants will generally be able to converse in some English or readily be able to find someone else who can.
Nevertheless, the farther outside of Montreal you go (Montreal is the English-speaking centre of Quebec and has the largest population of English speakers in the province), the less likely it is that the people you encounter can speak to you in English. If you do decide to venture out into less urban Quebec destinations, you should have an English/French dictionary or verse yourself with some basic French for travellers.
Beyond where you will or will not be able to find English speakers in Quebec, keep in mind that language in Canada is a touchy topic with a long, often hostile, history between English and French speakers that includes armed conflict and two provincial referendums in which Quebeckers voted on seceding from the rest of Canada.
Some tourists to Quebec - especially Quebec City - claim to detect underlying antipathy toward English speakers manifesting itself by way of poor or neglectful customer service. Having travelled more than 20 times to Quebec, I have to say I've never encountered such treatment, at least not more than anywhere else in Canada.
Overall, visiting Quebec requires no different planning than any other destination; however learning a bit of the language is part of the fun (after all, speaking French just feels glamorous) and may be helpful when you are off the beaten path.