Air Canada specifies that a personal item can include a backpack, briefcase or laptop computer measuring up to 16 x 33 x 43 cm.
EasyJet Flexi: Maximum size of 45 x 36 x 20cm which will need to be placed under the seat in front.
Conclusion: Mini Boss at 48.3cm L x 16.5cm W x 33cm is personal size! Just don't pack it to the brim.