This has been tested on a virtual guest with multiple virtual adaptors provided by the host (no vlans). It may work with linux virtual adapters (e.g. ens10:1) too but untested.
Default adaptor and gateway are as normal. No changes required.
The other two adaptors:
Add a route in on /etc/iproute2/rt_tables by adding the following to the bottom of the file:
ip route add default via 10.67.89.11 dev ens19 table rt2
ip rule add from 10.67.89.254/32 table rt2
ip rule add to 10.67.89.254/32 table rt2
ip route add default via 10.67.89.10 dev ens20 table rt3
ip rule add from 10.67.89.253/32 table rt3
ip rule add to 10.67.89.253/32 table rt3
You may wish to run tcpdumps on each interface:
tcpdump -nn -i ens20
tcpdump -nn -i ens19
tcpdump -nn -i eth0
Then connect on speedify and run a speed test to check that all windows scroll data and it is using all the connections.