Translation:The Canadian engineer is fixing a house.
"The Canadian engineer fixes the house" is acceptable there. I can think of almost no instance where the present tense cannot be substituted for the present progressive. Yet, Duolingo has a weird obsession with the present progressive because it's more common. Fix your translations.
I think only the present progressive is accepted to stress the nature of the partitive. The engineer is currently in this very moment fixing the house because that is what the partitive implies. I think I've also read (not sure if it's just a mnemonic though) that the partitive is used when the engineer is fixing the house is this very moment because we can't know if he will ever finish or whether he will only have fixed a part of the house in the end.
'Kanadalainen insinööri korjaa talon' could be used for "The Canadian engineer repairs the house". But 'Kanadalainen insinööri korjaa taloa' needs the continuous aspect, "is repairing" or "is fixing".
Korjaa isn't a partitive verb, the sentence isn't negative, and talo isn't an uncountable noun. So the only reason for talo to be partitive here is if the sentence is expressing an ongoing action.