This message is not a complaint , but a solution for those of you who wants to use the Sierra Wireless modem in Canada over the Rogers LTE network.
Just plug the card, watch it appearing in /Interfaces , LTE tab, and configure the APN to Lteinternet.apn , then apply .
Next, configure a D.H.C.P. client with this new interface ( LTEx ) , do your Masquerade on this interface and create a route 0.0.0.0 to it .
Reboot the beast ! That`s it , it should work,
Have fun, Serge ve2abc 
Well do you have any suggestions for what to do if the LTE connection does not appear in the interfaces tab?
Hello (I understand this is an old post) - would you please explain what exactly is not compliant? I took your suggestion and I was able to connect. Thank you
He probably means “this is not a complain” which means his post is not about a problem he is having.
Completely misread that. My apologies. I am having trouble with an RB751U-2HnD device running 6.11 with an external MC7700 Sierra Card. Connects just fine with the information above - trouble is, always asserts itself as the default route, despite “add default route” not being checked off. I tried via the CLI as well as the GUI and same issue. Does not honour the distance metric either 
I sent an email to support - but haven’t heard back.
I thought I would just update this thread as I made some comments on the default gateway. That is configurable via the DHCP-CLIENT attached to the LTE interface. Working very well. Uldis at Mikrotik responded to the support email I sent in. Thank you everyone.