Some 200 Canadian soldiers are already deployed in Ukraine as part of a training mission, which the defence minister said should be expanded.
Ukraine previously estimated that Russia had amassed about 100,000 troops near its border with Ukraine. Mr Reznikov said that number could soon grow to as much as 175,000.
Western intelligence and open-source data have shown a large amount of weaponry and ammunition on the move across Russia, and a large amount of equipment already stationed near Ukraine.
Volodymyr Zelenskiy, the Ukrainian president, on Monday visited the front line in the east where he presented medals to the troops.
“I am confident that with people like you we will win,” he said.
Russia’s ‘red lines’
German magazine Bild reported unverified intelligence data over the weekend, claiming that Russia seeks to seize two-thirds of Ukraine’s territory.
President Putin last week said that the idea of Ukraine joining Nato was a “red line” for Moscow, and it wanted iron-clad guarantees that Kyiv would never be allowed to join the alliance.
Moscow views Nato troops and weaponry on Ukrainian soil as an unacceptable threat to its security, Mr Putin said.
The Russian leader will hold a virtual meeting with US President Joe Biden on Tuesday in an effort to ease the tensions.
This is the second meeting for the two presidents since June when Mr Putin and Mr Biden sat down for talks in Geneva and agreed to launch negotiations on arms control and cyber security.
Bilateral talks behind closed doors have reportedly kicked off but with no visible progress yet.
Dmitry Peskov, Mr Putin’s spokesman, said Russia was willing to offer its own security guarantees for the West in return for a firm “legal agreement” that Kyiv will be kept out of the transatlantic alliance.
“Clearly, security guarantees cannot be unilateral,” he said.
Both Nato and Ukraine have insisted that Moscow has no right to tell other nations how to organise their defence strategies.
Relations between Moscow and Kyiv have been in crisis since 2014, when Russia annexed Crimea and gave its support to separatist rebels in Eastern Ukraine. The move left large swathes of Ukraine’s industrial heartland under control of Russia’s proxy forces.
Deadly fighting in the region largely stopped after a 2015 peace deal but Denis Pushilin, leader of one self-proclaimed republic, warned on Monday of a return to “large-scale hostilities”.
Mr Pushilin, along with Leonid Pasechnik, another separatist leader, were in Moscow over the weekend where they were made members of President Putin’s ruling United Russia Party at an annual congress.