No, not unless the person whose posts you want to see opted into bridging their account.
If both parties bridge their accounts they can follow eachother, or if one person bridges their account others can follow them.
I don’t think you can see boosts of stuff not on your platform though, and I don’t know how interacting with a bridged account works if both of you are bridged. If only the person you’re following is bridged they definitely won’t see it, but I don’t know if that changes if you’re both bridged
You opt in by following the bridgy fed account for your platform, so for Mastodon that’d be: https://bsky.brid.gy/bsky.brid.gy
There’s one on each platform, and when you follow it it’ll create you a bluesky/mastodon counterpart and send you the link to that bridged account
