Hi T Now, I'm not an accoustic engineer, but this was a big issue to us on our first house, for which I did some research on ways to reduce this noise.....so I know where you are coming from! :-)
Road noise is classified as 'white noise'.....a mixture of all frequencies, kind of like ocean noise, with high frequency providing most of the annoyance.
High frequency can be blocked with modest barriers such as storm windows, storm door and tall patio fences. However, mid range and the lower rumbles require sheer mass for shielding. Vinyl, foam, insulation bats, vegitation and screen doors offer little shielding. Brick or stone, as a facade to the house or a tall garden wall is the only real solution to this, that I can think of.
As to active sound cancellation, I have no experience. I have a friend who uses that as a passanger in small aircraft, but don't have any idea how that would work in a large living area.