I have another brother MFC. But drivers don't work. Only on Debian ...
Have you tried with using netcat for printing? nc <PRINTERIP> 9100 < filename ? In addition, I used cups and chose generic ipp anywhere. I had originally chosen generic PCL, but that didn't do color or double sided--not that I've ever needed to print doublesided, but it's nice to have the option.
For scanning, I did install sane-airscan. However, the package message says that you have to have avahi_daemon running, and I didn't do that, but still when I ran scanimage -L it mentioned something it read
device `airscan:w0:Brother MFC-L3780CDW series' is a WSD Brother MFC-L3780CDW series ip=192.168.1.50
So, I'm not sure if that means it needed airscan or would have worked without it. I installed sane-airscan before I got the printer, as I'd seen this thread on the forums where it solved someone's problem scanning with Brother.
I recently set up a MFC-J470DW Brother printer. I had trouble setting up the scanner (network) using the official bother drivers. I am currently using Linux compatibility and I got it working with 'Jessie'. The printer drivers are no longer required with CUPS as the 'everywhere' driver is...
forums.freebsd.org
My own thought on this is opensource has just gotten a lot better, for both printer and scanner to work more or less out of the box. With my old Samsung, I think somehow I got a printer driver (maybe used the Linux one?) and had to research getting the scanner running (found it from an ArchLinux wiki article, I had to change a line in /usr/local/etc/sane.d/xerox.mfp_mfp.conf.
I was worried after ordering the printer that it wouldn't work with FreeBSD and I'd only be be able to use it with Linux and only after installing Brother drivers, but that wasn't the case.