YYZ-HKG-SIN comes in at approximately 9398 miles , so round trip will be 18,796 miles.

Spending miles earned will be 18,796 plus 25% business class bonus giving approximately 23,495 miles

For status earning , you earn 1.5 qualifying points per mile flown in business class , so 18,796 plus 50% gives approximately 28,194 points. 25,000 qpoints is needed to attain AA Gold status ( which also gives OW Ruby status) so this trip will get the status

For points use, I would suggest that AA is probably the best option, so crediting there seems a good choice

Dave