For the most part, you should not mix oil paints and acrylic paints together before adding them to your canvas. Acrylic paints contain water while oil paints contain oil, so inherently these two don't work well together as have different properties and different needs, like drying times and varnish needs.
Though, if you want to paint one over the other, that is totally possible. However, it is best to paint oils over acrylics rather than the other way around.