It depends on the MKV. Most are encoded with the borders cropped and many are encoded with too many reference frames. As a result, if you make an AVCHD straight from most MKVs, it won't play in your blu-ray player or PS3.

To make a viable AVCHD you need:

a resolution of 1920x1080 or 1280x720;
four reference frames or fewer for 1080p;
six reference frames or fewer for 720p;
AC-3 or lpcm audio - though DTS seems to work with my player;
to use profile 4.1 - though 5.1 now seems to work on the PS3.

Most of the time, you will need to transcode. This can be done with multiAVCHD or uncropMKV, both by a developer called Dean. The former has many options, but the latter is simple, so I tend to use that.

I recommend one-pass turbo as the setting, as the slower/multi-pass settings take many days and you can't usually tell the difference. I also recommend that you don't exceed four B-frames or the encoding will be very slow: I use three.

I hope this helps!