To find the area of a Canadian football field, we first need to add the area of the American football field (6.4 x 10^3 square yards) to the additional area (3,350 square yards).
First, we convert 3,350 square yards to scientific notation:
3,350 = 3.35 x 10^3 square yards.
Next, we add the two areas together:
\[ 6.4 x 10^3 + 3.35 x 10^3 = (6.4 + 3.35) x 10^3 = 9.75 x 10^3 \text{ square yards}. \]
Thus, the area of a Canadian football field is:
\[ \boxed{9.75 \times 10^3} \text{ square yards}. \]