Is there a simple way to make a MIDI track not seem so mechanical?   I have gone to the PRV and edited the lengths of the sound bites  a more or less random  fashion and accomplished what I need to do, but is there an easier way?

As a rule, if all the notes are the same volume, then the off-beats will sound subjectively louder than the onbeats. So adjust accordingly. This seems to apply to halfs, quarters, eighths, sixteenths, or any length.

Humanize.cal?

Frank's Midi Plug-Ins - the humanize one.
http://www.midi-plugins.de/
 

Play the part with feeling.
There's really no hope for entering data and expecting it to sound like a real musician played it unless you are very skilled and knowledgeable about exactly what it takes to create great music . Of that I'm glad because it makes all the hard work I put into being a musician worthwhile. The day a machine sounds like me is the day the music truly will die. 
Go ahead and try the Humanizing logarithm, it will only add machine generated mistakes to the perfectly mechanical part. It cannot add feeling or create what only a skilled musical would play. 
 

This depends on many factors, not just the start position of the note, or speed.
Each VST used will have its idiosyncrasies.
Some sample libraries will be more realistic than others, containing true legatos, expression, staccatos, etc.
So everything will depend on a good choice of which VST / Library and how you know to make the most of what it offers.

Exact start and end time seems less important than sensitive, listening, adjustment of note volume, both at the attack and through the duration of longer notes.   I agree that 'humanize.cal' does not really work very well; but 'play it in' doesn't always work either, since that introduces a lot of new variables, including your finger-on-keyboard technique and the vagaries of your samples.    So, my method is to focus on volume adjustments using note velocity (if your VST accepts that as a factor) and CC11 (or CC1 or CC7, depending) as a changing of the amplitude during note playback, on the one hand, and using the Tempo View to draw in subtle tempo changes all the time.   
 
Using 'Copy Special' you can copy the tempo curve for a few moments or a few bars, and 'Paste special' puts the copied tempo curve into a new place.   Just be very vigilant for changes in what you think you've selected ... Sonar is weird that way. 

If it's for drums, and you use AD2, you can record the rhythm (or drag it, but it's a bit glitchy and I'm currently speaking about the drag function with XLN, who seem completly confused you can do it) into beats section. From their you have the 'Transform' tools. Allowing you to adjust the accents, and introduce randomness to the velocities and timings. When you are happy, drag it out to the clip

I'm with Cactus, it will only sound human if it's played by a human.

"Easy"? Sorry, no. There is really just one way to make MIDI tracks sound natural: play and record them in real time.
 
There are tools for randomizing velocities and timing, but - and this is important - live performances, though imperfect, are NOT random. A drummer does not place each hit exactly on the grid, but the extent to which a hit lands before or after the grid isn't random. Same for a saxophone solo, a piano rhythm track, or for each of the 20 violins in an ensemble. Musicians often do not consciously know why they make those decisions, describing it by the vague term "groove".
 
This presents a serious challenge for the solo composer/recordist, who is not an expert player for every instrument he might want to use in a composition. Even if you are an excellent guitarist, maybe even an excellent keyboardist as well, chances are you know little about tubas, celli or cajóns. However, the answer is the same regardless of your skill level: play each part by hand in real time, even if it takes a few tries to get it right.