1 AC 850 J6 C6 Z3 Y1 M1 U1 B1 /YYC LHR 3 1805 1000+1E0/333
H0 V0 Q0 L0 A0 K0 N0 I3

2 BA 119 F9 A9 J9 C5 D5 R4 I4 /LHR 4 BLR 1425 0515+1E0/744
W9 E9 T8 Y9 B9 H9 K9 M9 L9 V9 S9 N9 Q9 G9

I think for this you would maybe have to go through a TA or try multicity. I will try for you but wanted to post first to show you the availability.

Expensive is that the AC flight only has availability in high booking classes. Still less expensive than LH would chrage you when buying a ticket on day of departure...