Montreal is considered to be one of the safest cities in North America, boasting low violence rates and extremely friendly people. The streets are often filled with locals who are willing to help you get around, so it is unlikely that you will encounter any issues during your time there. Exploring tourist attractions at night should not be a problem either.
But as with any populous city, crime isn’t completely non-existent. Take precautions to ensure that you don’t encounter any problems. Remain vigilant and keep an eye on your belongings. Avoid poorly lit streets and always trust your intuition. Lastly, never carry large quantities of cash.
Travelling alone in Montreal should be fine too, whether you are a male or female solo traveller. As mentioned, take the precautions you would normally do when travelling and keep your valuables tucked away.