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